A yearlong national survey showed a “disturbing” amount of discrimination against deaf and hard-of-hearing would-be renters and led to the filing of nine federal fair-housing administrative complaints by advocacy groups and calls for better training of those who deal with individuals with hearing impairments.

So-called matched-pair testing by the National Fair Housing Alliance and affiliated groups often resulted in the hearing-impaired person being treated less favorably than the hearing person. Some rental agents simply hung up and refused to speak with a caller when told the person was serving as a relay for a deaf or hard-of-hearing individual. Others offered better rental terms to those who didn’t have trouble hearing. But Terrell Brittain didn’t need the survey to tell him that, the Houston Chronicle (sub. req.) reports.

A professor of American Sign Language interpretation at the University of Houston, he himself is deaf and has faced similar discrimination. At one time, weary of being cut off, he said at the beginning of each phone call: “Don’t hang up or I will file a federal complaint,” Brittain tells the newspaper. As a college student, he would be asked to wait as rental agents helped others ahead of him. “I wanted equal access,” he said. “I arrived here first. They should wait.”

The survey found that one in four of the 117 large companies investigated in 2013 discriminated, the Chronicle reports.

“The results of this investigation would seem to indicate that there is a problem with poor training,” said Howard Rosenblum, who serves as CEO of the National Association of the Deaf. “The extent of discrimination found in this investigation is disturbing.”

A National Fair Housing Alliance press release provides further details about the survey and the administrative complaints filed with the Department of Housing and Urban Development against large apartment companies and rental agencies in six states.